There has been a rapid increase in demand for refrigeration systems that can attain a very low temperature range. One type of system that can reach such temperatures is known as an ultra-low temperature freezer (“ULT”), which can maintain a very low range of temperatures. The ULT can be used to store and protect a variety of objects including critical biological samples, for example, so that they are safely and securely stored at a desired temperature for extended periods of time within a storage cabinet or compartment of the ULT. However, with the low storage temperatures involved, and the need to periodically insert and remove particular samples from the interior of the storage cabinet, various problems may arise.
Generally, in refrigeration systems, a refrigerant gas is compressed in a compressor unit. Heat generated by the compression is then removed generally by passing the compressed gas through a water or air cooled condenser coil. The cooled, condensed gas, is then allowed to rapidly expand into an evaporating coil that is in fluid communication with a refrigerator or freezer compartment where the gas becomes much colder, thus cooling the coil and the compartment of the refrigeration system or freezer with which the coil fluidly communicates.
Ultra-low and cryogenic temperatures ranging from approximately −95° C. to −150° C. have been achieved in refrigeration systems. An example of an ultra-low temperature freezer capable of reaching such temperatures is shown in U.S. Pat. No. 6,397,620 entitled Ultra-low Temperature Freezer Cabinet Utilizing Vacuum Insulated Panels, which is hereby expressly incorporated herein by reference in its entirety.
A method for constructing conventional ULT's may include forming an outer sheet metal cabinet and an inner metal cabinet and then applying expanded urethane foam to join the outer and inner cabinets to one another. This process is time consuming, messy and has inherent variation. For example, the two sheet metal cabinets may have to be placed in a large foaming fixture and urethane foam may be sprayed between the two cabinets. The foam is then allowed to cure, with typical required curing times being in the range of about 4 to about 48 hours, depending on the sizes and shapes of the two cabinets. The urethane foam provides insulation to the freezer.
There is a need, therefore, for construction methods and structures that address the problems and inefficiencies of conventional ULT's and conventional construction methods for producing such freezers and which can still provide support for the low temperatures achieved by the ULT.